1. Field of the Invention
The present invention relates to a method of treating electrically conductive waste contaminated with nuclear fuel materials and disposed from a nuclear fuel handling facility, and an apparatus for carrying out the method. More specifically, the present invention relates to a method of treating contaminated metallic waste produced when a nuclear fuel handling facility is dismantled, such as waste steel materials contaminated with nuclear fuel materials, or an adsorbent used for adsorbing nuclear fuel materials mounted in a nuclear fuel handling facility, and an apparatus for carrying out the method.
2. Description of the Related Art
FIG. 20 is a typical view of an apparatus for carrying out an electrolytic polishing process generally used for decontaminating waste contaminated with radioactive substances, such as nuclear fuel materials, (hereinafter referred to as "radioactive contaminated waste") by electrolysis. As shown in FIG. 20, a radioactive contaminated waste 3 is held by a holding device 2 and is immersed in an electrolytic solution contained in an electrolytic vessel 1 of a stainless steel. The radioactive contaminated waste 3 functions as an anode. A cathode 4 is immersed in the electrolytic water solution 5. When the radioactive contaminated waste 3 is a stainless steel waste, a phosphoric acid solution is used as the electrolytic water solution 5 serving as a bath. When the radioactive contaminated waste 3 is a carbon steel material, a sulfuric acid solution is used as the electrolytic water solution 5. The holding device 2 and the cathode 4 are connected to a dc power supply 6. When a dc voltage is applied across the holding device 2 and the cathode 4 by the dc power supply 6, the radioactive contaminated waste 3 functions as an anode. A surface layer of the radioactive contaminated waste 3 dissolves in the electrolytic water solution 5 simultaneously with coming off of radioactive contaminants adhering to the radioactive contaminated waste 3. Part of substances came off the radioactive contaminated waste 3 remains in the electrolytic water solution 5 and the rest is precipitated in sludge 8 on the bottom of the electrolytic vessel 1. Hydrogen 7 is produced on the cathode 4 of a stainless steel.
Generally, when decontaminating a radioactive contaminated waste by the electrolytic polishing process using the electrolytic water solution 5 as a bath, current is unable to flow uniformly over the entire surface of the radioactive contaminated waste when the radioactive contaminated waste has a complicated shape because the resistance of the bath is high. Consequently, the decontaminating effect of the electrolytic polishing process is reduced for some portions of the radioactive contaminated waste. If a high current is supplied to the bath to enhance electrolytic processing speed, heat is generated in the bath due to the high resistance of the bath. Hydrogen 7 produced on the cathode 4 during the electrolytic polishing process cause problems in safety. It is difficult to remove radioactive substances accumulated in the waste electrolytic water solution 5, particularly, radioactive substances dissolved in the waste electrolytic water solution 5 from the waste electrolytic water solution 5. The waste electrolytic solution 5 cannot be reused and becomes an additional radioactive contaminated waste. Thus, the total amount of radioactive contaminated waste increases.
The present invention has been made to solve those problems and it is therefore an object of the present invention to provide a method of treating waste from a nuclear fuel handling facility, capable of easily decontaminating a contaminated waste having a complicated shape, not discharging any effluent, capable of repeatedly using an electrolytic solution and not producing additional waste.
Another object of the present invention is to provide an apparatus for carrying out the foregoing method.